The present invention relates to an autonomous or controlled robot ball capable of moving in various environments, including indoors, outdoors as well as the planetary bodies such as planets and the Moon.
Upon designing a robot, the main difficulty is to make it sufficiently robust to sustain all environmental and operating conditions: shocks, stairs, carpets, various obstacles, radiation, thermal fluctuations, or direct manipulation of people or other robots, etc. The prior art wheeled robots can turn upside down and, then, be incapable of returning to the operational position. Other solutions to this problem are to use wheels bigger than the body of the robot, or a lever mechanism that can “flip” the robot in the right position. Alternatives to these solutions are to use a flat, rectangular shaped robot with tracks on each side, this will allow the robot to flip over and thus continue because of the tracks on both sides.
Yet an alternative and very competitive design is the ball robot concept as described in the following prior art patents: U.S. Pat. No. 6,227,933, U.S. Pat. No. 6,414,457, SE 517 699, DE 19617434, DE 19512055, DE 4218712 and WO 97/25239. Such a ball robot generally comprises a spherical shell and a drive mechanism enclosed in the shell. The locomotion principle of a ball robot is based on the disturbance of the system's equilibrium by moving its center of mass. By designing the drive mechanism such that it can rotate about the main axle 360 degrees in both directions, the displacement of the centre of mass brings the robot in motion back or forward, depending on the direction of rotation.
The prior art ball robots can be divided into two major groups:                Pendulum type comprising a main axle connected diametrically to the shell and supporting a drive mechanism arranged to drive a ballast pendulum for rotation around the main axle.        Shell drive type with a drive mechanism that is supported by and moveable along the shell inner surface.        
Moreover the report “ARIANDA AO4532-03/6201, Biologically inspired solutions for robotic surface mobility” gives a good overview over prior art ball robots of both types. The designs disclosed therein comprises:                ball robots of pendulum type with a telescopic main axle that makes it possible to alter the shape of the shell,        a ball robot with a hollow main axle, used as housing for scientific instruments, and        a ball robot of pendulum type wherein the main drive motor is placed in the pendulum and drives the pendulum for rotation about the main axle through a drive belt arrangement, thereby lowering the centre of mass for the robot.        
Ball robots of shell drive type have a major drawback in the sense that they are particularly sensitive to shocks. In harsh terrain or by force applied from the outside, the driving mechanism is easily damaged.
Ball robots of pendulum type are therefore considered more robust, especially when the pendulum is short and thus the centre of mass high.
FIGS. 1 and 2 show an example of a prior art ball robot of pendulum type. The ball robot 10 comprises a spherical shell 20 enclosing a drive mechanism 30. The drive mechanism is supported by and arranged to rotate around a diametric main axle 40 attached to the shell at respective ends. Due to the displacement of the pendulum centre of mass when driven for rotation about the main axle, the ball robot is put into motion. Moreover, the robot may comprise additional equipment in the form of analysis, monitoring, or actuator systems. The shell may be a perfect spherical shape, and/or multi-facetted shell with from a minimum of 10 to 30 sides. The shell can be elongated or shaped in any way as long as one main axis that is suitable for rotation around is preserved. The outer surface of the shell can further be provided with a pattern to prevent the ball robot from slipping, sliding sideways or the like
Drawbacks of such prior art ball robots of pendulum type is that the ability to traverse large obstacles, i.e. more than 25% of the radius in size from still standing is very low. Solutions with the centre of mass (CM) in the geometrical centre or close <15% of the radius from the geometrical centre of the ball robot will be limited in traversability because the ability to traverse is proportional to the ratio between the distance from the centre of the sphere to the CM to the sphere radius.